Isoproterenol (IPR), a beta-adrenergic drug, stimulates DNA synthesis in the parotid and submandibular glands. Repeated injections of this drug produces hyperplastic and hypertrophic enlargements of these organs. It is proposed to test the hypothesis that IPR may act as a tumor promoter in chemical carcinogenesis of the salivary glands. The possible tumor-promoting effect of IPR will be tested with two carcinogens, dimethylbenz(a)anthracene and methyl nitrosourea. The carcinogens will be given in low doses, followed by the chronic administration of IPR. Methyl nitrosourea will be given also at the peak of DNA synthesis induced by IPR, in order to test the significance of DNA synthesis in the carcinogenesis by this agent.